Air conditioning refers to the heating, cooling, cleaning, humidification and dehumidification of air. The most prevalent air conditioning systems employ vapor compression cycles, in which heat is pumped from one environment to another via a refrigerant that operates under two different pressure regimes so that the temperature can be increased when heat needs to be rejected to the environment or decreased when heat is to be absorbed by the refrigerant. The pressure difference in these systems is maintained by means of a mechanical compressor. This compressor is powered using electricity. The vast majority of air conditioning systems in commercial use employ the vapor compression cycle.
The principal limitation to the vapor compression cycle is that it is for all intents and purposes a sensible heat rejection device with minor capabilities to address the latent heat needs of a building. This is because the vapor compression cycle is only able to change the temperature of the air. Given this, the prevalent manner in which vapor compression air conditioning systems address the latent heat of a building is by reducing the temperature of the air to a point below its dew point and by removing water through condensation. In most cases, the air must be reheated in order to arrive at the desired building supply air temperature. This process is energy intensive.
Methods for dehumidification of the air conditioning incoming air have been invented and proposed. Among these is the use of a liquid desiccant loop coupled with an evaporative cooling system to generate cooling and dehumidification without requiring cooling the air to the dew point. These systems are designed using a plate heat and mass transfer arrangement in which liquid desiccant flows within selectively water permeable membranes that are attached to flat plates. The liquid desiccant flow absorbs moisture from air being dehumidified and then transfers it to a separate air stream that absorbs this moisture from the liquid desiccant. The air being dehumidified drops in temperature, cooling the air being dehumidified. Multiple plates stacked together form the heat and mass transfer device.
The plate arrangement has advantages in that it allows for a single device that does both air cooling and dehumidification using liquid desiccant streams. An example of this is described in US Patent Application, US 20100319370A1, titled “Indirect evaporative cooler using membrane-contained liquid desiccant for dehumidification.”